In communication networks, test signals or test messages are exchanged between the nodes of the network when establishing and during operation of connections, for example in Internet connections or connections to the signaling system no. 7 (SS7 protocol). This involves testing, for instance, whether the connection between two nodes is still physically present, whether the transmission quality of the connection is acceptable and whether there is data consistency between the two nodes. If the test fails, the connection is normally cleared and, for example, re-established via other nodes. Such a connection changeover involves very complex control and signaling procedures, which load the network heavily, in particular if the node is already heavily loaded by high message traffic.
In a test, a node sends test messages via the existing connection to another node, and receives from this node a response to this or an acknowledgement of its test message. Owing to internal problems in a node, it can happen that an incoming response or an acknowledgement cannot be evaluated. For example, if an overload occurs in a node because more messages are arriving than can be processed, message loss may occur and the received acknowledgement may be lost. Furthermore, it is possible that the test message to be sent is lost within the node and is not even sent. The lack of a response to the sent test message, however, can lead to the conclusion that the connection no longer physically exists, whereupon the connection is cleared even though the connection may not be at fault.
To overcome this problem, it is known to send the test message a second time after a wait time t in the absence of a response to a test message, as is specified, for example, in the ITU standard in Specification Q.707 for the periodic link test.